In the methods for controlling an operation mode of a hybrid electric vehicle in the related art, possible operation modes and conditions of switching from one operation mode to another operation mode are provided and then the hybrid electric vehicle is switched from one operation mode to another operation mode according to the conditions. However, there are following problems in the related art. (1) Problems of frequently switching from one operation mode to another operation mode are not considered. For example, when only using a state of charge (SOC) and an expected torque as controlling parameters, if the methods for controlling an operation mode in the related art are adopted, it may result in faults of continuously switching among some operation modes. (2) The SOC is controlled simply by only considering general operation conditions without considering a vehicle starting process. For example, during the vehicle starting process, if the SOC is slightly lower than a target value, a pure motor operation condition may be adopted and the vehicle has a good comprehensive performance at this moment. If the SOC is far lower than the target value, the pure motor operation condition cannot be adopted to avoid a fault that the battery is under charge. However, this phenomenon is not taken into account in the related art. (3) At present, the conditions of switching from one operation mode to another operation mode are constant, which cannot be calibrated and even goes against an actual vehicle calibration. For example, the changing of the operation mode may result in an operating efficiency of an engine improving and the power consumption increasing. In some operation conditions, although the operating efficiency of the engine is improved significantly, fuel economy of the vehicle is poor due to the increase of power consumption of a battery and a motor. Thus, during a process of determining threshold values, the increase of power consumption and the improvement of operating efficiency should be considered comprehensively. However, it is not taken into account in the related art, either. (4) The consideration is not comprehensive. The methods for controlling an operation mode in the related art provide ten or more operation modes. Since there are so many operation modes, it is hard to judge whether these operation modes can be distributed properly in a coordinate plane of the SOC and the expected torque, among which operation modes the vehicle may be switched and whether the specific switching conditions are correct or not, which resulting in the vehicle failing to operate in the optimal state in real-time and affecting the fuel economy of the vehicle.